I have always played and owned 4x12's. Blues, classic rock covers, progressive metal originals, lead guitar fill-in's for other bands, the works. Always had and used two 4x12's, when i was gigging heavily i had three 4x12's - two 5150 cabinets and a NOS 1983 Marshall lead 800 with original G12-65's that i used for medium to upper level volumes.
i normally liked the sound of 1 cabinet more than two for high volume playing, for low volume playing i actually prefer the sound of two 4x12's. I already sold my marshall cabinet, and i am currently getting ready to sell both of my 4x12's.
The main reason is i prefer the sound of impulses/studio polishing for mic'ed tracking. For the smaller gigs, i plan to bring a 2x12 stereo cabinet and run the tremoverb/5150 II in stereo. For larger venues and band practice, two VHT 4x12 cabinets and also keep the cabinets for when i get back into gigging heavily.
Each have their ups and downs, honestly stage room and the quality of the house PA dictates which i bring to a show and how much. It is quite nice to be able to point one cabinet at the drummer and the other at myself and be able to hear one another clearly - no volume battles. The other added benefit is combating the loss of stage volume outdoors, i cannot count how many times having 4x12's on stage allowed me to actually hear what i was playing and stay in pitch when i was to sing.
Downside is that much smaller venu's and most club owners see the 4x12's as a cocky assholish setup. I see it more and more these days, which is the other reason i am downsizing for now before building back up in the future when money and time and the gig's call for it.
Also, i invested in a set of hand trucks and ramps for my truck. no back breaking for me. If stairs were involved, i bummed a friends 2x12 marshall cabinet or bought a friend a 6 pack for a favor.